The present invention relates to a method of forming multilayer composite thermoplastic panels with a glossy finish using roller forming.
Roller forming as described in copending application Ser. No. 843,343, is a viable process for solid phase forming of thermoplastic sheet into large deformed panel shapes which could be used for automotive exterior body applications or building panels. Monolithic, that is, unreinforced, thermoplastic sheets which originally had a glossy surface finish can be formed into a panel type part with the same glossy finish as the original sheet. However when attempting to apply the same forming process to compos ite sheets, that is, glass fiber reinforced thermoplastic sheets, problems arise. The problems do not involve the actual forming of the composite sheet but rather that the final surface finish on the composite sheet is not glossy, even when the original composite sheet had a relatively glossy surface finish.
The reason for this degradation in surface finish when composite sheets are used, can be observed when the sheet is being heated prior to forming. The composite sheet, due to its method of fabrication, contains a considerable amount of trapped air beneath the surface. Upon heating, the trapped air bubbles rise to the surface and pockmark the surface. In addition, as the sheet surface softens during heating, the glass fibers which are usually constrained by the polymer matrix are free to poke through the surface. Thus, the surface finish is damaged simply by heating the sheet, and if anything, roller forming slightly improves the final surface finish. The composite panel could be finished by coating the panel with a glossy layer or paint. However, this would involve at least one additional finishing step.
It is an object of the present invention to provide a method of forming composite thermoplastic panels with a high quality glossy surface finish without adding any additional finishing steps.